The fabrication of wafers for electronics typically requires forming patterned layers of photoresist on the wafers which facilitate the formation of electronic circuits thereon. The patterns of photoresist are formed by shining light onto the photoresist through a patterned mask called a reticle. Since the pattern of the reticle is many times larger than the corresponding pattern required on the wafer, the image formed by the light must be reduced before reaching the wafer. Each wafer may require more than 30 different reticles during fabrication, so that a typical wafer manufacturing line processing several different parts may require thousands of reticles to be stored and available for use. The storage unit must keep particles or contaminants off the reticles because such contaminants can adversely affect the fabrication process and cause defects on the product wafers.
The present invention is directed to a reticle storage system including a reticle rack having a series of lateral slots, each for storing a reticle. Access to the reticles is provided on a lateral side of the rack. The enclosure has a series of doors for providing auxiliary manual access to the reticles in the slots. An air circulation system flows filtered air past the reticles in the rack to prevent contaminants from accumulating on the reticles. The air circulation system is capable of providing positive air pressure within the enclosure with one door open, thereby preventing contaminants from entering the enclosure through the open door.
In preferred embodiments, the reticle rack has a linear row configuration. The reticle rack is formed of rack modules which are capable of being stacked and positioned in a linear row. In one embodiment, the slots are configured to space the reticles about 0.65 inches apart from each other and the reticles are held by static dissipative material. The air circulation system provides a first air flow through the slots of the reticle rack and over any reticles stored therein. A second air flow transverse to the first air flow is provided adjacent to the lateral side of the rack. The first air flow can be about 30 ft./min. and the second air flow can be about 90 ft./min.
A robot is positioned within the enclosure for removing reticles from and replacing reticles in the reticle rack. The robot includes a drive system for driving the robot. A controller for controlling the drive system of the robot calculates a profile of a commanded motion just before the motion is performed. The motion is performed only when the controller determines that the motion can be performed. The controller may be required to recalculate the profile multiple times until the controller determines that the motion can be performed. Typically, the profile is calculated in sections. The robot further includes a gripper arm for gripping the reticles. The gripper arm is driveable by a gripper arm drive, away from and towards the reticle rack. The robot has a vertical column to which the gripper arm is movably mounted. Vertical movement of the gripper arm relative to the vertical column is capable of being provided by a vertical drive. The robot has a carriage to which the vertical column is rotatably mounted. Rotary motion of the vertical column is capable of being provided by a rotary drive. A gripper arm counterbalance for counterbalancing the gripper arm is housed within the vertical column to minimize particle generation and to be positioned near the center of mass of the robot. The drive system includes a bottom drive for driving the carriage of the robot alongside the reticle rack. In one embodiment, the drive system can include a top drive so that the robot can be driven from the top and the bottom, thereby providing precise vertical orientation.
The robot also includes a vision system for determining whether a slot in the reticle rack is occupied or empty, the position of the gripper relative to the slot, and whether the gripper is correctly gripping a reticle. The enclosure includes a robot service location for servicing the robot. The robot service location is capable of being isolated from the reticle rack to prevent contamination of the reticles during service of the robot. A pod opening system is included for placing reticles into and removing reticles from pods with the robot. An emergency access manual tool can attach to the reticle rack for removing and replacing reticles with minimal particle generation.